Recovery of valuable products from spent sulphite liquors



Patented Apr. 23, 1929.

UNITED STATES I 1,710,272 PATENT OFFICE.

. GEORGE A. RICHTER, 0F BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY,

OF BERLIN, NEW HAMPSHIRE, A. CORPORATION MAINE.

RECOVERY OF VALUAIBLE PRODUCTS FROM SPENT SULPHITE LIQUORS.

No Drawing.

This invention relates to the recovery of valuable products from spent digesting liquor, being more particularly related to the recovery of valuable products from spent liquors resulting from the digestion of cellulose-fiber-bearing material in sulphurous acid solutions of ammonium salts.

When cellulose fiber bearing material, such as wood, is digested in a sulphurous acid solution of a soluble sulphate and/or sulphite under prescribed conditions of time, temperature and chemical concentration, there is produced a sulphite pulp of low ash content, suitable for the manufacture of high grade papers and for the preparation of a high alpha-cellulose-containing fiber. l/Vhen sodium sulphateand/or sodium sulphite' are employed as the chemicals in the fiber-liberating sulphurous acid solution, the spent liquor resulting from digestion is separated from the pulp, neutralized preferably with basic sodium compounds, e ap orated to the desired concentration, and then delivered to a combustion retort wherein its organic content is burned and its inorganic content smelted in a reducing or oxidizing atmosphere, depending on the chemicals which it is desired to recover. The smelted chemicals may be delivered from the retort into a bod of water to produce a smelt solution W ich may then be subjected to further treatment for the preparation of an alkaline or acid digesting liquor, depending upon the conditions which were maintained in the retort. When, on the other hand, ammonium sulphate and/or ammonium sulphite are employed as the chemicals in the fiber-liberating sulphurous acid solution, the spent liquor resulting from digestion is sep arated from the pulp, but, in lieu of smelt ing the valuable combined nitrogen or ammonium compounds thereof as in the case of sodium compounds, is, in accordance with the process of the present invention, neutralized, preferably with basic calcium phosphate, and then evaporated to dryness but without smelting the ammonium compounds, for l. have found that the residuum is admirably adapated for use as a fertilizer.

The spent liquor resulting from digestion in a sulphurous acid solution of ammonium salts contains fixed nitrogen in the form of the original salts, i. e., sulphate and sulphite, and also in the form of organic ammonium sequently processed.

Application filed January 6, 1927. Serial No. 159,501.

compounds, as ammonium ligneous sulphonates. If digestion has been effected in a sulphurous acid solution of essentially only ammonium sulphate as described in my application, Serial No. 159,243, filed Jan. 5, 1927, because of the stability of the sulphate under digesting conditions, the resulting spent liquor contains substantially the fixed nitrogen content of the fresh digesting liquor. In addition, the liquor also contains the nitrogen and otassium removed from the wood during digestion. After the separation of the pulp from the spent liquor, such liquor is neutralized, preferably with basic calcium phosphate, so as to increase the fertilizing value of the product as well as to produce a neutral liquor which will not corrode apparatus in which it is sub- The neutral liquor is then evaporated to the desired concentra: tion and finally dried to form a flaky or pulverulent residuum. Such a flaky or pulverulent residuum is suitable for sale as a fertilizer, not only because of its finely divided physical condition, but also because the fertilizing elements therein exist in a form readily available for plant nutrition.

A specific example of procedure which may be followed in producing the product of the present invention may be substantially as follows. After completing digestion in. a sulphurous acid solution of an ammonium salt, i. e., an'nnonium sulphate and/or ammonium sulphite, the digester contents are blown in a blowpit. Chemicals such as S0,, which are emitted from, the blow, may be recovered, if desired, by any approved method. The pulp is separated from the spent liquor and may then be subjected to such further processing as may be desired.

The separated acid spent liquor is then neutralized prior to the evaporation of a portion of its aqueous content, such neutralization preferably being effected with basic calcium phosphate rock. Such rock is readily obtainablc on the market and not only serves as a relatively inexpensive neutralizing agent, but also as an excellent and Y a rapid neutralizing action with the acid content of the spent liquor.

'In certain-instances where it' is desirable to increase the potassium content of the product available as fertilizer, a potassium compound which reacts to form a plant nutritive, or which in itselfi without reaction v a plant-nutritive salt, is employed as the po tassium-supplying compound. The addition "of such potassium compound to the acid spent liquor may be efiected together with the addition of the basic phosphate.

The neutral spent liquor is evaporated to,

.say, about a "concentration, as by means of multiple-etiect evaporators, whereupon the concentrate is delivered to a drum dryer, a hot air spray dryer, or other suitable form oi drying apparatus, which removes the watcr content of the concentrate and produces a flaky or pulverulcnt residuum. Such a residuum is in suitable form for sale as a fertiliner, the fertilizing elements, viz, fixed nitrogen, phosphorus and potassium, existing therein in a form available as plant nutrients.

It also contains the organic encrusting matter removed from the wood chips, such organic material enhancing its fertilizing value by decomposition in the soil into humus, carbon dioxide, and other products which stimulate plant growth and maintain the soil in a loose, porous condition.

In lieu of adding potassium-bearing material to the spent liquor, if desired, such material, e. g.,potassium carbonate or potassium sulphate, may be employed together with the ammonium salts in the fresh sulphurous acid digesting solution. Also, a certain amount of phosphorus-bearing material, e: g., basic calcium phosphate, may be added, together with such potassium-bearing mate rial. Potassium carbonate reacts with-the free sulphurous acid to form potassium b1- 'sulphite, which functions ,as an excellent fibereliberating agent, being equivalent in this respect to sodium bisulphite. Potassium sulphateremains essentially as such in the digestingliquor, only a small proportion. f thereof initially being convertedto potassium bisulphite by inetathetical reaction with thQSlllplTUIOllS acid, but as the potassium bisulphite is progressively consumed or spent by reaction, more potassium sulphate is' progressively converted into potassium bisulphite, Basic calcium phosphate reacts with the sulphurous acid solu- -.tion to form superphosphates and. calcium bisulphi te, The superphosphate is probably sin-inactive constituent of the cooking liquor, but the phosphorous constituent therein is in a form available for plant nutrition and apears in such form in the spent cooking iquor. The calcium bisulphite is, of course, an active fiber-liberating agent. The spent liquor resulting from digestion is neutralized, concentrated, and then dried to form a flaky or pulverulent product, as hereinbefore outlined.

Av process such as herein described permits digestion of cellulose-fiberc0ntaining material to be carried out on a practical commercial scale in sulphorous acid solutions of ammonium salts, since the valuable fixed nitrogen content of the fresh digesting liquor may be economically recovered from the spent digesting liquor and in addition economically fortified by other fertilizer elements, such as phosphorus and potassium. When digestion takes place in a sulphurous acid solution of essentially only ammonium sulphate, the spent liquor contains substantially the equivalent of the fixed nitrogen content of the fresh cooking liquor, as ammonium sulphate is substantially stable at digesting temperatures. Such nitrogen content of the spent liquor is augmented by the potassium and nitrogen content removed from the cellulose-fiber-bearing material. The process of the present invention eliminates the necessity of smelting and associated recovery apparatus necessary when digestion is effected in sodium salts, and also makes possible the production of sulphite pulp without necessitating the pollution of streams or river-s, such as takes place when digestion is carried out in calcium bisulphite liquors, the spent liquors from such latter process of digestion being largely wasted by discharge into flowing Water and injuring piscatorial life and constituting a general nuisance.

I do notherein claim the process of digesting cellulose-fiber-containing material in sulphurous acid solutions of ammonium sulphate, as this is disclosed and claimed in my application for patent hereinbefore referred to. i a

What I claim is:

1. A fertilizer comprising the residuum of spent liquor resulting from the digestion of cellulosic material in a sulphurous acid solution of ammonium salts, said residuum including substantially all the organic matter removed from such cellulosic material.

2. A fertilizer comprising the residuum of spent liquor resulting from digestion of raw cellulosic material in a sulphurous acid substantially all the organic matter removed from such cellulosic material.

4. A fertilizer comprising the residuum of spent liquor resulting from digestion of raw cellulosic material in a sulphurous acid solution of ammonium salts and containing potassium-containing material, said residuum including substantially all the organic matter removed from such cellulosic material.

5. A fertilizer comprising the residuum of spent liquor resulting from digestion of raw cellulosic material in a sulphurous acid solution of ammonium salts and containing phosphorous-containing material, .said residuum including substantially all the organic matter removed from such cellulosic material.

6. A fertilizer comprising the residuum of spent liquor resulting from digestion of cellulosic material in a sulphurous acid so lution of ammonium salts and containing potasslum-containing material and phosphorus-containing material, said residuum including substantially all the organic matter removed from such cellulosic material.

7. A fertilizer comprising the residuum of spent liquor resulting from digestion of cellulosic material in a sulphurous acid solution of ammonium salts and neutralized with basic calcium phosphate.

8.- A fertilizer comprising the residuum of spent liquor resulting from digestion of cellulosic material in a sulphurous acid so lution of ammonium salts and neutralized with basic calcium phosphate and treated with potassium-containing material.

9. A fertilizer comprising the residuum of spent liquor resulting from digestion of cellulosic material in a sulphurous acid so-- lutlon of ammonium salts and neutralized.

with basic calcium phosphate and basic p0- tassium-containing material.

10. A process which comprises neutralizing the spent liquor resulting from digestion of cellulosic material in a sulphurous acid solution of ammonium salts with basic cal cium phosphate, evaporating and drying the neutralized liquor, and recovering the residuum.

11. A process which comprises neutralizing spent liquor. resulting from digestion of raw cellulosic material in a sulphurous acid solution of ammonium salts, treating the spent acid liquor with basic calcium phosphate and potassium-containing material, evaporating and drying the neutralized liquor, and recovering the residuum.

12. A process which comprises neutralizing spent liquor resulting from digestion of raw ccllulosic material in a sulphurous acid solution of ammonium salts with basic calcium phosphate and basic potassium compounds, evaporating and drying the neutral liquor, and recovering the residuum.

13. A process which comprises neutralizing spent liquor resulting-from digestion of cellulosic material in a sulphurous acid solution of ammonium salts with basic calcium phosphate, evaporating and drying the neutralized liquor to produce a pulverulent or flaky residuum, and recovering the residuum.

14. A process which comprises neutralizing with 7 basic calcium phosphate spent liquor resulting from digestion of cellulosic material 1n an acid solution of ammonium salts, and recovering the solids content of the neutralized liquor.

In testimony whereof I have afiixed my signature.

GEORGE A. RICHTER. 

